Measuring physical features of lenses is important for determining appropriate design and manufacturing aspects of lenses. This importance is particularly significant in the design and manufacture of vision correcting lenses, such as contact lenses, intraocular lenses, corneal onlay lenses, corneal inlay lenses, and spectacle lenses, where the lenses are produced to correct or enhance a patient's vision.
Typically, when vision correcting lenses, such as contact lenses, are being measured, it is necessary to physically section or cut the lens. For example, to examine a thickness profile of a contact lens, it is necessary to cut the lens along one or more meridians and then obtain an image of the cross-section of the lens. Frequently, the sectioning of the lens is only performed along a single meridian and therefore, in order to obtain an accurate thickness profile map of the contact lens, it is necessary to cut many individual lenses from among a batch of lenses.
To determine or examine the curvature of a lens, such as a contact lens, the curvature is estimated by placing the lens on a planar surface so that the physical distance from the lens edge to the highest point of the lens can be measured to determine the sagittal height of the lens. The sagittal height can then be used to estimate the curvature of the lens. Although such a method may be useful in determining the curvature of a spherical lens, the method becomes less accurate as non-spherical lenses are being examined. Another method of estimating lens curvature includes the use of a keratometer. For example, a keratometer can be used to estimate lens curvature by measuring two reflected images reflected from the back surface of the lens.
Thus, there remains a need for new methods which enable a lens to be measured, such as without physically cutting a lens, and that provide accurate surface measurements of both spherical and non-spherical lenses.